1. Field of the Invention
The present invention relates to an improvement for a television receiver which magnifies the images displayed on the receiver screen to persons viewing the television.
2. Description of the Prior Art
Various lens systems have been devised to attempt to magnify the images on a television receiver screen so that television viewers can watch the television screen from a distance without an excessive loss of detail in the image. The purpose of such systems is to allow persons to view televised programs or television sets having small screens without sitting extremely close to the television set or to enhance the details which they are able to see. One such magnification system is disclosed, for example, in U.S. Pat. No. 2,449,886. However, conventional television screen magnification systems have proven unsatisfactory for several reasons.
The lens systems which have been employed in conventional television receiver image magnification devices have caused excessive distortion and aberrations in the images which they magnify. The magnification achieved is not uniform, so that the image observed is significantly distorted and different parts of the image which are observed across the face of the magnification system differ greatly in proportion. As a consequence, conventional magnification systems have never achieved significant commercial success since the images observed have always been so distorted.
A further disadvantage of conventional television screen image magnification systems is the high directional sensitivity of such systems. Indeed, unless an observer is located almost directly in front of such a magnification system for a television receiver so as to observe the image along a line of sight substantially coincident with the axis of the kinescope tube of the receiver, portions of the image observed are highly distorted and indeed images at the corners of the magnification systems are often unrecognizable. If one attempts to view a television screen through a prior art plano-convex lens magnification system, the image can only be observed within forty five degrees from either side of the axis of the kinescope tube of the receiver. If a viewer is positioned more than forty five degrees from the center line of the kinescope axis, as measured from the intersection of that axis with the outermost surface of the magnification system, no image can be seen. The same is true when viewing a television screen through a prior art magnification system which employs only a Fresnel lens.
This disadvantage renders the devices unsatisfactory in many viewing situations, where the functional and aesthetic placement of furniture within a room prohibits seating along a line of sight coincident with the kinescope axis, and where a television receiver is viewed from several different locations within a room. As a result, while a person seated directly in front of the television receiver observing the image through a conventional magnification system along a line of sight substantially coincident with the kinescope axis will observe images which are magnified with only moderate distortion, other observers seated only slightly to the side of the kinescope axis will observe images which are highly distorted.
A further disadvantage of conventional television receiver magnification systems is that the magnified images are produced faithfully and without substantial distortion only when viewed from a particular distance from the receiver. When the television receiver is viewed from distances either closer to or further from the optimal distance for which conventional magnification systems are designed, substantial distortion and significant aberrations appear.
Prior art television receiver magnification systems, such as that described in U.S. Pat. No. 2,449,886 do not produce a uniform magnification of an image. The portions of the image at the center of the television screen are disproportionately magnified relative to the portions of the image at the periphery of the screen. Thus, for example, if an image of a human being is displayed full length upon the television screen, the head and feet of the individual viewed through a conventional magnification system will appear disproportionately small and the waist and midriff section of the individual will appear excessively large. Similarly, if an automobile image is displayed at full length on a television screen the passenger compartment will appear excessively large, while the front and rear fenders and bumpers will appear disproportionately small. Such distortions are characteristic of an image viewed through a plano-convex lens or a Fresnel lens alone.
A further disadvantageous feature of plano-convex lenses as employed for magnifying images from a television screen is that such lenses magnify not only the televised image of interest, but also the raster of horizontal broadcast scanning lines. These horizontal scanning lines are so narrow and closely spaced together in a conventional television screen as to be unobjectional when the image on the receiver screen is viewed at normal size. However, when the image is magnified by only a plano-convex lens, both the width and the separation between the broadcast scanning lines is magnified.